Recent technological advancements in weapons systems have led to more effective munitions, and new methods of firing or deploying such munitions. Computerized weapon sighting systems have also been developed to provide rapid solutions to ballistic problems so that a trajectory path to a target can be computed, and a gun aimed accordingly. Such sophisticated computerized weapon sighting systems are also able to aim or position the weapon appropriately so that the accuracy of a hit on the target is optimized. Exemplary of such types of fire control systems are U.S. Pat. Nos. 3,575,085; 3,689,741; 4,318,330; 4,312,262; 4,418,361 and 4,528,891.
In the more sophisticated weapon sighting systems, a gunner or operator can view both a target and superimposed thereon an indication of the position of the weapon or gun barrel. The gun position indication is generally cross hairs or a reticle. In this manner, a gunner or operator need only view a single display, and yet be able to maintain the weapon trained on the target, even though the target may be moving.
As noted, the positional indication of a weapon is normally a reticle which has a vertical scale and an intersecting horizontal scale. The reticle is similar to cross hairs, the intersection of which indicates the exact position in which the weapon must be aimed in order for the projectile to hit the target. Various approaches have been taken to generate and superimpose a weapon sighting reticle on the target. In military armament, such as tanks, the weapon sighting system is normally periscope-type equipment. In this type of system, the weapon is aimed directly at the target, without regard to azimuth, windage, atmospheric conditions or the type of projectile. A computer then solves a ballistic equation by using the noted variables, and provides a solution related to the direction in which the weapon should be directed in order for the projectile to hit the target. In accordance with the solution of the ballistic equation, one of the mirrors in the periscope arrangement is tilted so as to displace the reticle with respect to the target. The gunner simply moves the gun so that the target and reticle are again aligned, whereupon a projectile fired from the newly positioned weapon will follow the correct trajectory. The disadvantage with this approach is that the mirror in the periscope apparatus must be gimballed and controlled with gyroscopes which require maintenance, are delicate and susceptible to damage, and are costly.
Another approach used in weapon sighting systems for superimposing a gun sight reticle on a target is illustrated in U.S. Pat. Nos. 4,318,330; 4,312,262 and 4,418,261. In sighting systems of this type, a cathode ray tube (CRT) is utilized to generate a reticle at any position on the CRT face. An optical system is employed to superimpose an image of the reticle on a target image. To aim the weapon, the computer drives the CRT according to the solution of a ballistic equation to displace the reticle on the CRT face. The reticle image is thus also displaced with respect to the target so that the gunner can reposition the weapon and realign the target and reticle image. In the practical application of the CRT sighting system, continued readjustment is required to maintain the weapon correctly calibrated with the fire control system. This is mainly due to vibration and temperature affects on the CRT equipment which affect the deflection system thereof and thus cause instability problems.
In other types of weapon slighting systems, the reticle is constructed using a mechanical vertical and horizontal needle, each mechanically moveable under control of the computer to change the position of the cross hairs. Again, by virtue of the mechanical apparatus involved, reliability is of critical concern.
From the foregoing it can be seen that a need exists for an improved reticle generation system which is economical, reliable, durable and thus not susceptible to damage, nor require periodic maintenance.